PASSENGERS should not expect Scotland’s beleaguered rail service to hit key punctuality targets for more than two years, an official report has said.

Network Rail bosses admitted trains will continue to fall short of punctuality and reliability markers until at least 2021-22.

It comes as the Office of Rail and Road (ORR) gave the green light to a £4 billion package aimed at improving Scotland’s railways.

Scottish Labour’s transport spokesman Colin Smyth said the ORR was “confirming what Scotland’s rail passengers already know – this is a failing franchise with no prospect of hitting its performance targets any time soon”.

He said: “Passengers deserve better than this plummeting performance. It’s time Scotland’s railways were taken back into public hands, so passengers not profits are put first."

Rail punctuality is measured by the Public Performance Measure (PPM), which records the number of trains arriving at their final destination within five minutes of the advertised time.

ScotRail has repeatedly come under fire for missing its PPM target of 92.5 per cent, and recently logged its worst performance in more than two decades.

Bosses previously said they would not hit the required PPM target until the end of 2019-20 – but the ORR’s latest report reveals this has been pushed back even further.

It states: “[Network Rail] now considers it is unlikely to achieve PPM of 92.5% until year three of CP6 [2021-22]. For years one and two it is forecasting PPM of 90.5% and 91.5%.”

Publicly-owned Network Rail, which runs the railways, is part of a joint venture with train operator ScotRail.

Despite the poor outlook, the ORR said it would keep the 92.5% target in place while recognising “some potentially significant risks”.

Meanwhile, the regulator paved the way for Network Rail to push forward with its five-year, £4bn plan to improve the railways and boost punctuality and journey times.

John Larkinson, chief executive of the ORR, said this meant “Network Rail, the Scotland route and the system operator can now implement their plans to deliver a service which passengers and freight customers rightly demand and deserve”.

He said: “These plans are focussed on improving performance for passengers and freight operators by getting the basics right – ensuring that the railway is properly maintained and renewed, and on improving the daily operation of the railway.”

Alex Hynes, managing director of the ScotRail Alliance, said: “We welcome this news from the regulator which secures continued investment in our infrastructure and shows confidence in our plans.

“Network Rail is committed to putting the needs of customers at the heart of the service the rail industry provides in Scotland and we’ll work hard over the next five years to deliver a better and more reliable railway for our passengers and freight operators.”

But a Transport Scotland spokeswoman said there are a "number of issues which are still to be finalised”.